Through use of tritiated thymidine-labeled spermatozoa and autoradiographic techniques at light- and electron-microscopic levels, the movement of sperm DNA in blastodiscs of domestic fowl ova will be traced, and the role of the spermatozoon at the initiation of development thus assessed. These experiments are designed to determine the cause(s) of the extraordinarily high incidence of abnormal embryonic development that follows certain manipulations of semen (involving temporal and quantitative factors and the site of insemination). At the same time, these experiments will expand studies already in progress in my laboratory but hitherto almost completely neglected, on events in the avian ovum during the first minutes and hours after ovulation, and thus including actual processes of sperm penetration, syngamy, initiation of cleavage etc. Use of tritiated thymidine-labeled semen can pinpoint instances of gynogenesis; since prelimanary results suggest the possible importance of such instances an additional technique, use of semen from a mutant that produces an electrophoretically identifyable embryonic hemoglobin, will be employed to explore this relation to abnormal embryonic development.